Field of the Invention
Embodiments of the invention generally relate to power conversion and, more particularly, to power converter surge protection.
Description of the Related Art
Power converters connected to an AC power grid are required via government standards to survive power surges from the grid-side and thus must survive both simulated lightning strikes as well as real ones. A typical standard that must be met by such power converters is ANS1 C62.41. To meet the standard, a power converter must handle a voltage amplitude as high as 6000 v, open circuit, and a current amplitude as high as 3000 A on a short circuit. In order to survive these simulated surges, power converters must either survive the 6000 v (which is rarely feasible) or dissipate the energy while clamping the voltage to a survivable value.
Typical voltage protection networks used in power conversion involve clamps such as, for example, metal oxide varistor (MOV), Zener and other solid state devices.
FIG. 1 depicts a schematic diagram of a background art ladder network 100 used for surge protection. The ladder network 100 comprises inductors 102 and 104, and Zener diodes 106 and 108, using the Zener diodes 106 and 108 to form a clamp. The inductor 102 is coupled across first terminals of the Zener diodes 106 and 108, and the inductor 104 is coupled across second terminals of the Zener diodes. The Zener diode 106 is coupled across a circuit, such as a power converter, and the Zener diode 108 is coupled to a power grid.
FIG. 2 depicts a schematic diagram of a background art multistage ladder network 200 used for surge protection. The multistage ladder network 200 is a protection network having multiple stages and additional filtering capacitors with respect to the ladder network 100. The protection network 200 comprises inductors 202, 204, 206, and 208; capacitors 212, 214, and 218; and Zener diodes 210, 216, and 220. The inductor 202 is coupled across first terminals of the Zener diodes 210 and 216, and the inductor 204 is coupled across second terminals of the Zener diodes 210 and 216. The inductor 206 is coupled across first terminals of the Zener diodes 216 and 220, and the inductor 208 is coupled across second terminals of the Zener diodes 216 and 220. The capacitors 212, 214, and 218 are coupled in parallel across the Zener diodes 210, 216, and 220, respectively. The Zener diode 210 is coupled across a circuit, such as a power converter, and the Zener diode 220 is coupled to a power grid. The inductors in each of FIGS. 1 and 2 (i.e., inductors 102, 104, 202, 204, 206, and 208) can be common mode, differential mode or a mix. They help reduce the stress on the clamps by reducing the flow of energy. However, these inductors are generally wound on a core such as ferrite, powdered magnetic iron, and the like that cannot possibly handle the surge current and saturate quickly, thereby reducing their effectiveness.
In addition, electromagnetic interference (EMI) filtering often requires surge protection in the form of clamping devices (voltage clamping diodes, gas discharge tubes (GDTs), metal oxide varistors (MOVs), and the like). Such clamping devices drive up production costs and increased components mean less reliability with more points of circuit failure.
Therefore, there is a need in the art for an improved surge blocking inductor for use in power converters.